Re: [RFC PATCH] drivers: power: Add watchdog timer to catch drivers which lockup during suspend.

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Apr 30, 2013 at 08:36:21PM -0700, Colin Cross wrote:
> On Tue, Apr 30, 2013 at 4:30 PM, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> > On Tue, Apr 30, 2013 at 03:28:33PM -0700, Zoran Markovic wrote:
> >> From: Benoit Goby <benoit@android.com>
> >>
> >> Below is a patch from android kernel that detects a driver suspend
> >> lockup and captures dump in the kernel log. Please review and provide
> >> comments.
> >
> > There's this really cool thing called a watchdog driver that does stuff
> > like this :)
> 
> If the watchdog driver worked in this case this patch wouldn't exist.

Great, let's fix the watchdog timer then :)

What's wrong with it?

> >> Rather than hard-lock the kernel, dump the suspend thread stack and
> >> BUG() when a driver takes too long to suspend.  The timeout is set to
> >> 12 seconds to be longer than the usbhid 10 second timeout.
> >>
> >> Exclude from the watchdog the time spent waiting for children that
> >> are resumed asynchronously and time every device, whether or not they
> >> resumed synchronously.
> >
> > No, don't add a driver-core-only timer, use the existing watchdog timers
> > if you are worried about the kernel locking up.
> 
> The watchdog timers are useless here.  For one, they generally stop
> when their driver suspend op is called, so you may not even have one
> running when you lock up.

But you can fix that, right?

> More importantly, the purpose of this patch is to tell you which
> driver locked up and hopefully why, and the watchdog driver will
> usually result in a silent reset.

I thought it was an option as to what the watchdog does when it
triggers.

> This patch will cause a stack trace of the driver suspend op that is
> blocking suspend progress, even if that call does not happen in the
> suspend thread.

But who can see this, the machine is now dead.

greg k-h